I. Field of the Invention
The present invention relates to the interworking between Frame Relay and Asynchronous Transfer Mode (ATM) transmission schemes and, more particularly, to a system and method for allowing a FR DTE to communicate with another FR DTE or to an ATM DTE through wide area or local area ATM network, the communication through the ATM network being the Switched Virtual Circuit (SVC) service.
II. Background of the Invention
Over the past decade, many businesses, through growth and mergers, have dispersed their locations across the country and, in many cases, around the world. In the various business locations, local area networks (LANs) are used for interconnecting groups of people using PCs and workstations. As the popularity of LANs increases, so does the need for the interconnection of those LANs located across the country and around the world.
But as the size and geographic dispersement of these private networks grow, the interconnect expense increases. The cost and complexity of building and managing these private networks increase exponentially as more equipment, facilities and expertise is required.
Frame Relay is one of the most convincing transmission schemes in today's networking world. The Frame Relay is a frame based transmission technique and has gained a lot of support from the Data Terminal Equipment (DTE) vendors and the end user groups. Frame Relay, a "fast packet" multiplexing specification, is designed to create more efficient wide area networks (WANs) by permitting users to access only the amount of bandwidth they need for a given application. In addition, Frame Relay has been recognized as being able to improve LAN networking solutions by standardizing LAN interconnection techniques and by reducing the number of required leased lines in a network.
Frame Relay is a "connection-oriented" protocol. It establishes a logical connection for the duration of the call, and it is initially being implemented as a permanent virtual circuit (PVC) service. It is a data transport service that operates at layer 2 of the OSI reference model and uses variable length data packets.
Asynchronous Transfer Mode (ATM) has been chosen as the technology for use in the future and, in particular, for supporting Broadband Integrated Services Digital Nelwork (B-ISDN). It can support many types of services at a variety of speeds which makes its particularly appropriate for use with multimedia services that require multiple data channels operating at different speeds.
Frame Relay has emerged as one of the packet technologies in the United States for fractional T1 and T1 rates while ATM is being defined for future implementation at fiber and SONET rates of initially 155 Mb/s and later on 622Mb/s.
Because of evolutionary considerations, such as interface and protocol standardization and equipment availability, differences in performance characteristics, similarity in technology, and potentially common markets served, these two technologies will have to co-exist for some time. Thus, the interworking between Frame Relay and ATM network has become a very important issue.
The problem is that, because Frame Relay has been available for some time now, there are presently available DTE which is adapted for interfacing a network supporting the Frame Relay service, or supports the Frame Relay Interface (FRI). In contrast, however, ATM is relatively new and is not widely available, if available at all in many locations. As a result, presently, few DTEs are equipped with ATM support. Furthermore, the DTE supporting ATM (ATM DTE) that is available is relatively expensive and is somewhat redundant to the DTE presently installed that supports Frame Relay (Frame Relay DTE).
Furthermore, ATM provides additional transport capability that Frame Relay does not provide, such as for multimedia traffic. It would be desirable to utilize ATM transport capability with Frame Relay traffic. In most implementations. Frame Relay supports only the Permanent Virtual Circuit (PVC) connection mechanism and not Switched Virtual Circuit (SVC) connection mechanism. The ATM service supports both PVC and SVC connection mechanisms. Because PVC is more expensive than SVC (PVC is akin to a leased line while SVC is analogous to the dial-up link), it would be desirable for a FR DTE to have access to this less expensive form of data transfer. In addition, because some communication is real-time, such as interactive communication or multimedia data, the guaranteed arrival times and bandwidths of ATM are desirable and many times necessary. It would be desirable for a FR DTE to be able to communicate over ATM utilizing the less expensive SVC service while having the guaranteed arrival times and peak bandwidth for multimedia data.
Therefore, it is desirable to have a terminal adapter which will interface with the subscriber's Frame Relay DTE (via an FRI) and communications adapter and, on the network side, will interface with an ATM network to communicate with either a Frame Relay DTE or an ATM DTE. It is further desirable to have such a terminal adapter allow the Frame Relay DTE capitalize on the transport capability provided by the ATM to transmit delay/loss sensitive traffic, such as multimedia traffic, through the ATM network without adding any overhead through the use of the SVC connection mechanism.